Coating composition



' automotive finish.

Patented Sept. 10, 1940 PATENT OFFICE COATING COMPOSITION George R. Ensminger, New Brunswick, N. J. assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Dela were No Drawing. Application January 12, 1939,

Serial No. 250,527

'7 Claims.

This invention relates to, improved coating compositions and more particularly to cellulose nitrate coating compositions which are highly resistant to discoloration from direct contact with oils and greases.

Recent advances in thedevelopmentof cellulose nitrate enamels for automotive and industrial'finishing fields and particularly for the finishing of automobiles have provided outstanding improvements in general durability and more particularly in the elimination or reduction in chalking tendencies, a deficiency generally encountered in the earlier finishes when exposed .to the atmospheric elements. This defect has been largely overcome through the use of special or specially treated pigments or specific types of vehicles. .However, in certain instances, the finishes which exhibit improvements in chalk resistance have proven to be defective in their resistance to "oil spotting or discoloration when mineral oils or greases are brought in direct contact therewith.

This defect is particularly significant and more frequently encountered in automobile finishes where grease and oil may inadvertently come in contact with the finish during servicing and lubricating of the automobile before or after delivery to the consumer. lubricants are quite injurious in this respect. Oil spotting is also frequently caused by the oil containing rubbing compounds employed in conventional rubbing operations performed after application of the finish. Discoloration from this source is particularly apparent when the rubbing compound is permitted to remain .on the finish during temporary shut-down periods.

stitutes another source of discoloration of the The effect of such oil or grease on the finish is not a softening or destructive action on the film but rather an unsightly discoloration which is especially pronounced in the light colored finishes, including metallic finishes consisting of low pigmented enamels containing finely ground aluminum which are generally popular at the present time. The eifect seems to be permanent since it cannot be removed by any known cleaning or polishing means without removing excessive amounts of the finish and, therefore, presents a serious problem in the finishing of surfaces which may be exposed to contact with mineral oils and greases.

affords a finish that is highly resistant to oil spotting discoloration from direct contact with mineral oils and greases. Another object of the invention is the provision of a cellulose nitrate The new hypoid gear Fuel -oil from the exhausts of Diesel engine trucks concoating composition which affords a finish of superior outdoor durability. A further object of the invention is the provision of a cellulose nitrate coating composition which afiords a finish that may be readily rubbed and polished. A still' further object of the invention is the provision of a cellulose nitrate coating composition which affords a finish that is adherent, flexible and non-thermo-plastic under a bufifing wheel.

These objects are accomplished by means of a composition comprising definite proportions of cellulose nitrate, certain specific modified alkyd resins, plasticizers, and suitable pigments and/or other coloring matter.

The following examples in which the quantities of the ingredients are indicated inper cent by v weight illustrate the invention:

Example 1-White enamel The resin solution of the above example consists of a mixture of 30 parts by weight of toluene and parts by weight of a synthetic resin prepared as follows:

gredients:

. Pounds Coconut oil 45.0 Glycer 15.0

Heat to :2 I". and add:

Pound Caustic soda (dissolved in small amount of water) 0.10

Stir and heat to.460-4'70 F. until homogeneous and soluble in denatured ethyl alcohol.

Add:

Charge into a copper kettle the following in- Pounds G1ycerine 46.0 Phthalic anhydride 139.5 Dibutyl phthal'ate 75.0

Heat (covered) to 425 F. and add:

' Pound Cupric acetate (wetted with dibutyl phthalate) 0.1

Stir and continue heating at 425 F. until an acid number of 5 is obtained. The resin is then cut with toluene in the proportions previously indicated. The use of the copper kettle and the copper salt with the several advantages which accrue therefrom is described in U. S. Patent 2,103,238.

.The foregoing procedure provides a resin with approximately the following composition:

. Per cent Glyceryl triphthalatenn; 60 Coconut oil 15 Dibutyl phthalate 25 This resin composition may also be suitably prepared by other methods known in the art but since neither the resin per se or the method for its preparation comprises the present invention, description of alternate methods is not deemed necessary.

The enamel composition of Example 1, which contains cellulose nitrate, resin and plasticizer in the ratio of 10 parts by weight of cellulose nitrate, 5 parts by weight of resin and 4 parts by weight of plasticizer'is prepared by first dispersing the pigment in a cellulose nitrate colloid adjusted to a suitable consistency by the addition of solvents and diluents according to the process described in U. S. Patent 2,052,470- This pigmented intermediate is then placed in an agitator mixer together with the remaining ingredients, including the synthetic resin solution,

and the mixture thoroughly agitated until a homogeneous enamel product is obtained.

The synthetic resin of this composition and its preparation are the same as described under Example 1.

The above enamel contains cellulose nitrate, resin and plasticizer in the ratio of -10 parts by weight of cellulose nitrate, 2.5 parts by weight of the resin and 5.5 parts by weightof plasticizer and is prepared by the method described for Example 1 which involves dispersion of the pigment in the colloided cellulose nitrate portidn of the composition by suitable kneading action followed by the addition of the remaining ingredients which are incorporated by conventional mixing procedure.

. Other methods of dispersing the pigment-in the vehicles of the invention such as by grinding in ball mills, roller mills, buhrstone mills or from pigment pulps according to the process described in co-pending application to Robert T. Hucks, S. N. 91,965, may also be utilized if desired.

, Coating compositions previously employed for finishing automobiles and other. objects which might be exposedto mineral oils and greases comprising cellulose nitrate and modified alkyd resins were ineffective in preventing serious discoloration of the finish resulting from direct contact with mineral oils and greases, frequently causing consumer complaints or failing to pass,

final inspection in the production line in the manufacture of new automobiles. It is, therefore, essential to the success of the present invention that the specific requirements described herein be strictly observed, particularly as to the type of modified alkyd resin and its particular chemical composition and the relative amounts of cellulose nitrate, alkyd resin and plasticizer present in the enamel composition.

In preparing the bi-modified alkyd resins for the present invention, phthalic acid esters ofother alkyl and cyclic alcohols may be employed, for example, the phthalic acid esters of isobutyl alcohol, amyl alcohol, methoxy ethanol, ethoxy ethanol, butoxy ethanol, cyclohexanol, methyl cyclohexanol, and of a mixture of alcohols boiling above 0., all of which have a branched chain structure and which are obtained in the catalytic synthesis of methanol from carbon monoxide and hydrogen. Aprocess for the manufacture of the phthalic acid ester of the last mentioned mixture of alcohols is described in U. S. Patent 2,015,077.

The alkyd type resin should be modified with not more than about 40% and preferably not less than about 20% of the combined modifiers consisting of dibutyl phthalate or equivalent and coconut oil or similar non-drying oils such as cottonseed oil or blown oils of these types. The non-hydrox'y, non-drying vegetable oils are generally preferred because of the added durability which they impart particularly from the standpoint of superior chalk resistance. If the upper limit is exceeded to any appreciable extent when the oil ratio is on the high side of the dibutyl phthalate-oil ratio shown below, oil spotting tendencies become apparent and if this limit is much exceeded when the dibutyl phthalate is on thehi'gh side of the dibutyl phthalate-oil ratio, thermoplasticity is encountered during rubbing and polishing operations. Below 20% combined modifiers, the advantages of the invention are so reduced as to make the compositions of greatly reduced commercial significance.

In studying the effect of varying the two resin modifiers, it was found that the ratio of dibutyl phthalate to coconut oil is preferably about 1 to 0.6 parts by weight. If the coconut'oil proportion appreciably exceeds this ratio, oil spotting tendencies become apparent. On the other hand, if the proportion of oil is reduced to a ratiq of below 1 part of dibutyl phthalate to 0.2 part of coconut oil, thermoplastic tendencies are encountered during normal rubbing and polishing operations. The most operative range, therefore, lies between the ratio of 1 part by weight of dibutyl phthalate to from 0.2 to 0.6 part by weight of coconut oil.

The alkyl or cyclic alcohol ester of phthalic acid-non-hydroxy non-drying vegetable oil modified resin employed in the present invention may be readily manufactured with a low acid number and for the compositions of this invention, the acid number of the present invention is kept as low as possible, preferably not more than 5 or 6 and in any event not over 10. Reactive type pigments such as zinc oxide will not tolerate resins of high acid number because of poor can storage stability as evidenced by the formation of grit.

It is also essential in order to obtain maximum resistance to oil spotting combined with acceptable durability and satisfactory working properties that the cellulose nitrate-alkyd resin- .invention at hand.

plasticizer ratios be kept within definite limits.

These ratios should be such that for each 10 parts by weight of cellulose nitrate the amount of resin and polishing operations generally practiced in the automotive industry. The amount of plasticlzer present in the composition varies inversely with the amount of alkyd resin, thus establishingan operative ratio range of cellulose nitrate: al-

kyd resin: plasticizer of between 10:9:1 and 10:2.5:5. For maximum resistance to oil spotting combined with acceptable durability and satisfactory working properties, this ratio is be-' tween 10:7:3 and 10:5:5. In any event, the combined modified aliwd resin and free plasticizer content should not exceed an equivalent amount of cellulose nitrate and in general should be present in amounts not appreciably less than V; the amount of cellulose nitrate if the several benefits of the invention are to be secured.

The types and proportions of solvents and diluents shown in the examples may be varied over a considerable range and the substitution of an equivalent material or change in proportions to suit conditions of application or other special requirements is considered within the ordinary practice of one skilled in the art. The plasticizer ingredient may be composed of one or more of the conventional plasticizing materials such as tricresyl phosphate, dibutyl tartrate, dicyclohexyl phthalate, dimethyl cellosolve phthalate (dimethoxy ethyl phthalate) diethyl phthalate, etc.

Cellulose nitrate of low viscosity characteristic on the order of that indicated in the examples is preferred, but the use of commercially available cellulose nitrates of higher viscosity characteristics is in no wise precluded, since the several advantages hereinafter described likewise accrue.

Although phthalic anhydrideis the preferred acid radical in the alkyd resin ingredient of the improved compositions, certain other acids such as succinic, malic, adipic, etc., may be substituted wholly or in part for the phthalic anhydride, although bestresults are secured when phthalic anhydride is present in preponderant quantities.

Suitable resins for the new compositions may also be prepared using other polyhydric alcohols such as diethylene glycol, trimethylene glycol, sorbitol, diglycerol, etc.

The invention is operative with all types of coloring matter including pigments, dyestuffs and lakes, for example, zinc :oxide, iron blues, maroons, toners, carbon black, chrome yellows, chrome greens, etc., and is of particular merit with the lighter colored so-called pastel shade and metallic enamels. As indicated inthe examples, the particular pigment employed in the composition may have some influence on the ratios of the essential cellulose nitrate, alkyd resin, plasticizer ingredients on the basis of the oil absorption of.

the coloring matter, but any necessary adjustment in this respect is considered within the ordinary practice of one skilled in the art with the circumscribed limitations of the herein described The compositions of the invention are generally useful in finishing surfaces which may be exposed to direct contact with oils and greases. They are particularly useful for finishing automobiles where contact with lubricating oils and greases and oil containing rubbing compounds and polishes is more frequently encountered.

The new compositions have shown anumber of important advantages when employed in the sug- 5 gested utilities. In the first place, they'have exhibited an unexpected but very desirable high resistance to spotting or discoloration of the finish from oily rubbing and polishing compounds or from direct contact with oils and greases which 10 sometimes reach the finish of an automobile through careless servicing of the car before or after deliveryto the consumer. This defect of oil spotting was quite common in the commercial finishes heretofore available and caused frequent consumer complaint and costly rejections in the final inspection in the manufacture of newautomobiles. Furthermore, the new compositions aifordgood resistance to chalking tendencies,

thus preserving the original gloss and luster for 20 1 extended periods on exposure to atmospheric conlatedingredients are usually quite defective in 30 this respect, making them entirely unsuited for the present purpose. Substantial economies are represented in the new finishes as provided by the improved compositions in that assembly line rejections and consumer complaints necessitating 35 refinishing of automobiles because of oil spotting discoloration are practically eliminated.

As many widely diiferent embodiments of this invention may be made without departing from the spirit and scope thereof, it will be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

' 1. A coating composition highly resistant to 5 oils and greases comprising cellulose nitrate, an alkyd resin having an acid number below 10 modified with a non-hydroxy, non-drying vegetable oil and a phthalic acid ester of an alcohol selected from the class consisting of alkyl and cyclic 5o 1 alcohols and a plasticizer, the combined alkyd resin and plasticizer being present in an amount .by weight not exceeding an equal amount by weight of cellulose nitrate.

2. Composition of claim 1 in which the phthalic as acid ester is dibutyl phthalate.

3. Composition of claim 1 in which the nonhydroxy, non-drying vegetable oil is coconut oil. 14. Composition of claim 1 in which the alkyd resin is modified with about 15% of a nonso hydroxy, non-drying vegetable oil and about 25% of a phthalic acid ester of an alcohol selected from the group consisting of 'alkyl and cyclic alcohols.

5. Composition of claim 1 in which the modified 55 fied with a non-hydroxy,'non-drying vegetable oil and a phthalic acid ester of an alcohol selected from theclass' consisting of alkyl and cyclic alcohols and a plasticizer in the proportion by weight of between 10 parts of cellulose nitrate to Qparts of said resin to 1 part of plasticizer and.

-- fled with from 20% to 40% of a non-hydroxy,

non-drying vegetable oil and dibutyl phthalate in the proportion of between 0.2 and 0.6 parts of said oil for each part of dibutyl phthalate, and a plasticizer, said ingredients being present in the proportion by weight of between 10 parts of cellulose nitrate to 7 parts of said resin to 3 parts of plasticizer and 10 parts of celluloes nitrate to 5 5 parts of said resin to 5 parts of plasticizer.

GEORGE R. ENSMINGER. 

